Among the different bearings that support shafts undergoing rotative or rectilinear movement and make such movement smooth, the semi-spherical bearing is advantageous in that it is able to simultaneously support load in both the radial and axial directions. Accordingly, it is unnecessary to use separate bearings for each of the directions such that weight can be reduced, allowing application to internal motors in electronic goods such as computer hard drives, laser beam scanners, laser beam printers, etc.
With regard to the laser beam printer, laser beams are used to perform the printing operation. That is, a scanned image is formed on a photosensitive drum, which is responsive to light, by radiating the laser beams thereon. A rotating multi-faceted mirror system is provided to move the beams at a uniform velocity such that the beams are aligned on the photosensitive drum in an axial direction thereon.
Referring to FIG. 1, there is shown a sectional view illustrating a rotating multi-faceted mirror system in which a conventional semi-spherical bearing is mounted. As shown in the drawing, the rotating multi-faceted mirror system 10 comprises a multi-faceted mirror 11 which reflects beams onto a photosensitive drum (not shown), and a motor 20 for rotating and supporting the multi-faceted mirror 11. A housing 12 is provided encasing the multi-faceted mirror 11. The housing 12 includes a hole 12a through which the multi-faceted mirror 11 is exposed.
The motor 20 comprises a stator 21 and a rotor 22, electromagnetically cooperating with the stator 21. The stator 21 includes a stator frame 21a and a stator coil 21b wrapped around the stator frame 21a, while the rotor 22 includes a rotor bushing 22a and a rotor magnet 22b provided around a circumference of the rotor bushing 22a. A lens bracket 13, which fixedly supports the multi-faceted mirror 11, is mounted on an upper portion of the rotor bushing 22a such that the multi-faceted mirror 11 rotates together with the rotor bushing 22a.
A semi-spherical bearing 24 is inserted in upper and lower parts of the rotor bushing 22a such that the bushing is supported and able to rotate. The semi-spherical bearings 24 are fixed by a support shaft 23 provided through a center of the rotor frame 21a, the semi-spherical bearings 24 being disposed such that their spherical portions face one another.
A plurality of grooves 24a are formed on an outer circumference of the semi-spherical bearings 24 to allow for smooth rotation with the rotor bushing 22a. The grooves 24a, as shown in FIGS. 2 and 3, are spiral-shaped to allow for suction of air for smooth rotation.
However, in the above-described prior art multi-faceted mirror system, the manufacturing process of the bearings is complicated. Namely, a lathe is first used to form the semi-spherical shape, and then the grooves are formed at a predetermined depth using an etching process. Because many steps are needed in the process to manufacture the semi-spherical bearing, overall manufacturing costs are increased.
Further, wear occurs between the bearings and rotor bushing, especially when the rotor bushing starts and stops its rotation. This results in a reduction in the life span of both the bearings and rotor bushing. Also, the wearing of these two elements makes it necessary to use increasingly larger amounts of electricity to maintain the same level of rotational speed.